The present invention relates generally to temperature control arrangements for printheads and, more particularly, to a temperature monitoring system and method which switches a timer between multiple interrupts of a processor.
Thermal ink jet printer mechanisms which utilize printheads having heater resistors for effecting the ejection of small ink droplets from the printhead are well known. The ejection of a large number of small ink droplets at controlled locations on a printing medium produces a desired printed image. In such printheads it is desirable to control the overall temperature of the printhead in order to assure that ink droplets are delivered as desired. In order to control the printhead temperature it is of course necessary to measure or monitor the printhead temperature in some manner.
One manner of monitoring printhead temperature involves the use of one or more detectors located on the printhead. Various circuit arrangements and techniques incorporating various types of detectors can be utilized to produce temperature related signals from which the actual temperature of the printhead can be estimated or determined. One problem encountered in such arrangements is a need to read temperature related signals at specific times or intervals, even while a temperature calculation operation is taking place.
Accordingly, it would be advantageous to provide a temperature monitoring system and method which facilitates appropriate reading of temperature related signals without undue complexity or component cost.
In one aspect of the invention, a printhead temperature monitoring system includes a processor having a top priority interrupt input, a normal priority interrupt input, and at least one input for receiving temperature related signals. The processor is programmed or otherwise operable to calculate a printhead temperature based at least in part upon temperature related signals read on the input. A single timer circuit provides interrupt signals to the interrupt inputs of the processor. An interrupt control circuit is connected between the single timer circuit and the processor for selectively controlling application of timer circuit interrupt signals to the top priority interrupt of the processor and the normal priority interrupt of the processor.
In the foregoing arrangement, the interrupt control circuit may be used to deliver read triggering interrupt signals from the timer circuit to the top priority interrupt of the processor causing the processor to read a temperature related signal from the input, and to deliver temperature calculate triggering interrupt signals to the normal priority interrupt of the processor causing the processor to initiate a temperature calculation operation in a normal priority mode. During the temperature calculation operation of the processor, the processor is operable in response to a read triggering interrupt signal delivered to the top priority interrupt input to temporarily interrupt the temperature calculating operation in order to read another temperature related signal. In this manner the system assures that temperature related signals are read when necessary, but at the same time permits temperature calculating operations, which are not as time dependent as the temperature related signals themselves, to take place in a normal priority mode to reduce interference with other processor functions taking place during operation of a printer. Where a setup triggering interrupt signal is delivered to the top priority interrupt of the processor during a temperature calculating operation, the processor responsively temporarily interrupts the temperature calculating operation to perform a setup function such as clearing a counter.
In a preferred embodiment of the foregoing arrangement at least one temperature sensitive resistor is provided on a printhead and a capacitor is operatively connected to be charged through the temperature sensitive resistor. A voltage level detection circuit monitors a voltage level across the capacitor as it is charged and a counter associated with the voltage level detection circuit maintains a running count as the capacitor is charged until the voltage level across the capacitor reaches a threshold level. The count value in the counter is the temperature related signal. The top priority interrupt of the processor is an FIQ interrupt and the normal priority interrupt of the processor is an IRQ interrupt.
In another aspect of the present invention, in a printhead temperature monitoring method a step (a) involves establishing a signal which relates to a temperature of a printhead. After step (a), a step (b) involves applying an interrupt signal to a top priority interrupt of a processor which causes the processor to read the established temperature related signal. Subsequent to step (b), a step (c) involves applying an interrupt signal to a normal priority interrupt of the processor which causes the processor to initiate a temperature calculating operation. Subsequent to step (c), a step (d) involves (i) establishing a signal which relates to a temperature of a printhead, and (ii) subsequent to step (d)(i), applying an interrupt signal to a top priority interrupt of the processor which causes the processor to read the established temperature related signal of step (d)(i). During step (d)(ii) the processor temporarily interrupts the temperature calculating operation initiated in step (c) in order to read the temperature related signal of step (d)(i). Again, the subject method assures that temperature related signals are read when necessary, but at the same time permits temperature calculating operations, which are not as time dependent as the temperature related signals themselves, to take place in a normal priority mode to reduce interference with other processor functions taking place during operation of a printer.